\begin{tikzpicture}
    \pgfmathsetmacro{\factor}{0.5}
    \pgfmathsetmacro{\a}{3 * \factor}
    \pgfmathsetmacro{\b}{4 * \factor}
    \pgfmathsetmacro{\c}{5 * \factor}

    \begin{scope}
        \tkzDefPoints{0/0/B, \a/0/C, \a/\b/A}

        \tkzDrawPolygon(A,B,C)
        \tkzLabelPoints[above](A)
        \tkzLabelPoints[left](B)
        \tkzLabelPoints[right](C)
        \tkzLabelSegment[right](C,A){$b$}
        \tkzLabelSegment[below](C,B){$a$}
        \tkzLabelSegment[left](A,B){$c$}
    \end{scope}

    \begin{scope}[xshift=4cm]
        \tkzDefPoints{0/0/B', \a/0/C', \a/\b/A'}

        \tkzDrawPolygon[dashed](A',B',C')
        \tkzLabelPoints[above](A')
        \tkzLabelPoints[left](B')
        \tkzLabelPoints[right](C')
        \tkzLabelSegment[right](C',A'){$b$}
        \tkzLabelSegment[below](C',B'){$a$}
        \tkzLabelSegment[left](A',B'){$c$}
        \tkzMarkRightAngle(A',C',B')
    \end{scope}
\end{tikzpicture}

